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Abstract:

A battery pack thermal management system includes a plurality of battery
cells connected to at least one DC power bus. At least one thermoelectric
device is operatively disposed in thermal contact with the plurality of
battery cells. At least one temperature measuring device is operatively
connected to the thermal management system, and configured to measure a
temperature of a predetermined portion of the plurality of battery cells.
A cell balancing circuit is operatively connected to the plurality of
battery cells, and configured to selectively divert a portion of electric
current from at least one of the plurality of battery cells to the at
least one thermoelectric device. An electronic controller is operatively
connected to the cell balancing circuit, and configured to control a flow
of electric current to the at least one thermoelectric device.

Claims:

1. A battery pack thermal management system 10, comprising: a plurality
of battery cells connected to at least one DC power bus; at least one
thermoelectric device operatively disposed in thermal contact with the
plurality of battery cells; at least one temperature measuring device
operatively connected to the thermal management system, and configured to
measure a temperature of a predetermined portion of the plurality of
battery cells; a cell balancing circuit operatively connected to the
plurality of battery cells, and configured to selectively divert a
portion of electric current from at least one of the plurality of battery
cells to the at least one thermoelectric device; and an electronic
controller operatively connected to the cell balancing circuit, and
configured to control a flow of electric current to the at least one
thermoelectric device.

2. The battery pack thermal management system as defined in claim 1
wherein the electronic controller is configured to: compare the
temperature of the predetermined portion of the plurality of battery
cells to an upper temperature reference and a lower temperature
reference; and generate an upper error value and a lower error value for
the predetermined portion of the plurality of battery cells.

3. The battery pack thermal management system as defined in claim 2
wherein the electronic controller controls the flow of electric current
to the at least one thermoelectric device based on the upper error value
and the lower error value for the predetermined portion of the plurality
of battery cells.

4. The battery pack thermal management system as defined in claim 1
wherein the at least one thermoelectric device is disposed in thermal
contact with at least one thermally conductive structure opposed to the
plurality of battery cells.

5. The battery pack thermal management system as defined in claim 4
wherein the at least one thermally conductive structure is disposed in
thermal contact with a heat exchanging fluid.

6. The battery pack thermal management system as defined in claim 5
wherein the heat exchanging fluid is air or a liquid coolant.

7. The battery pack thermal management system as defined in claim 1
wherein the portion of electric current diverted is between about 0 mA
and about 200 mA per battery cell.

8. The battery pack thermal management system as defined in claim 1
wherein the at least one temperature measuring device comprises a thermal
imaging device, or at least one temperature transducer.

9. The battery pack thermal management system as defined in claim 1
wherein the at least one thermoelectric device is a Peltier device, and
the plurality of battery cells includes lithium ion battery cells.

10. A method for battery pack thermal management, comprising: balancing a
voltage of each battery cell in a plurality of battery cells operatively
connected to at least one DC power bus by shunting a portion of electric
current from at least one of the plurality of battery cells to at least
one thermoelectric device in thermal contact with a predetermined portion
of the plurality of battery cells; determining a temperature of the
predetermined portion of the plurality of battery cells; and controlling
a magnitude and direction of the flow of electric current flowing to the
at least one thermoelectric device, thereby heating or cooling the
predetermined portion of the plurality of battery cells.

11. The method as defined in claim 10 wherein the at least one
thermoelectric device is a Peltier device.

12. The method as defined in claim 10 wherein the controlling is based on
an upper error value and a lower error value respectively generated for
the predetermined portion of the plurality of battery cells by comparing
the temperature of the predetermined portion of the plurality of battery
cells to an upper temperature reference and a lower temperature
reference.

13. The method as defined in claim 12 wherein the portion of electric
current flowing to the at least one thermoelectric device is proportional
to the upper error value or the lower error value.

14. The method as defined in claim 10, further comprising actively
transferring heat between the predetermined portion of the plurality of
battery cells and at least one thermally conductive structure operatively
connected to the plurality of battery cells through the at least one
thermoelectric device.

15. The method as defined in claim 14, further comprising transferring
heat between the at least one thermally conductive structure and a heat
exchanging fluid.

Description:

TECHNICAL FIELD

[0001] The present disclosure relates generally to battery pack heating
and cooling systems and control thereof.

BACKGROUND

[0002] Battery cells in a battery pack are generally not completely
identical. Individual battery cells in a battery pack may tend to operate
at different temperatures and voltages even though the individual battery
cells are of the same model and time-in-service. Non-uniformity in the
voltage among individual battery cells has been balanced using resistive
loads. The energy dissipated by the resistive loads is generally wasted
energy. The service life of a battery may be deleteriously affected by
operation outside of a normal operating temperature band.

SUMMARY

[0003] A battery pack thermal management system includes a plurality of
battery cells connected to at least one DC power bus. At least one
thermoelectric device is operatively disposed in thermal contact with the
plurality of battery cells. At least one temperature measuring device is
operatively connected to the thermal management system, and configured to
measure a temperature of a predetermined portion of the plurality of
battery cells. A cell balancing circuit is operatively connected to the
plurality of battery cells, and configured to selectively divert a
portion of electric current from at least one of the plurality of battery
cells to the at least one thermoelectric device. An electronic controller
is operatively connected to the cell balancing circuit, and configured to
control a flow of electric current to the at least one thermoelectric
device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features and advantages of the present disclosure will become
apparent by reference to the following detailed description and drawings,
in which like reference numerals correspond to similar, though perhaps
not identical, components. For the sake of brevity, reference numerals or
features having a previously described function may or may not be
described in connection with other drawings in which they appear.

[0005] FIG. 1 is a schematic diagram depicting an example of a battery
pack thermal management system of the present disclosure;

[0006] FIG. 2 is a schematic diagram of an example of a control system in
an example of the system of the present disclosure;

[0007] FIG. 3 is a semi-schematic depiction of an example of a Peltier
device used in an example of the system of the present disclosure;

[0008] FIG. 4 depicts an example of a Li-ion battery used in an example of
the system of the present disclosure; and

[0009] FIG. 5 is a semi-schematic depiction of an example of a
thermoelectric device mounting relationship within an example of the
system of the present disclosure.

DETAILED DESCRIPTION

[0010] Electric Vehicles and Hybrid Electric Vehicles may include electric
batteries for storing electrical energy. The batteries may be charged at
a charging station, or by charging systems onboard the vehicle. Examples
of onboard charging systems include regenerative braking energy recovery
systems and generators powered by internal combustion engines. The
batteries may provide electrical energy for accelerating the vehicle and
for powering accessories including entertainment systems, instruments,
gauges and lighting, control systems, heating, ventilation and cooling
systems, and other electrically powered devices included in or connected
to the vehicle.

[0011] In order to store useable energy, a vehicle may have a battery pack
that includes a plurality of individual battery cells. The individual
cells in the battery pack may be connected in series, parallel or
combinations thereof. A state of charge (SOC) of individual battery cells
may vary relative to other individual battery cells in the same battery
pack. As used herein, the term SOC is based on the actual measured energy
content of a battery and is expressed as a percentage of the battery's
maximum rated Ampere hour (Ah) capacity (see, e.g., SAE J2711). The
variation in SOC from cell to cell may be caused by e.g., manufacturing
variability (resistance, capacity, self discharge, etc.), thermal
characteristics and monitoring circuit loads. SOC variation can result in
overcharge of cells with a high relative SOC. Cell balancing to actively
set all cells in a pack to substantially the same SOC may prevent
overcharge of cells that exhibit a high SOC without balancing. Preventing
overcharging of battery cells may improve useful life of the individual
cells and the entire battery pack.

[0012] A resistive cell balancing circuit, in which a resistive load is
added to a cell or group of cells may be used for SOC balancing. In an
example of resistive cell balancing, a resistive cell balancing circuit
could bypass up to 200 mA per cell. Except in cases where the resistive
heat is considered desirable and is usable, the bypassed 200 mA could be
considered as generating waste heat. (Recalling Joule's First Law: the
energy lost each second, or power, increases as the square of the current
and in proportion to the electrical resistance of a conductor.) Thus,
some of the usable energy of the battery pack may be substantially lost
without performing any useful function. Such energy loss aggregated for
an entire battery pack for a period of time could, for example, amount to
approximately 100 W-120 W of electrical power loss. As disclosed herein,
the electrical power from cell balancing may be used to power
thermoelectric devices to cool or heat battery cells and improve the
useful life of individual cells and the battery pack.

[0013] Referring now to FIG. 1, in an example, a battery pack thermal
management system 10 includes a plurality 20 of battery cells 25
connected to at least one DC power bus 23. At least one thermoelectric
device 30 is operatively disposed in thermal contact with the plurality
20 of battery cells 25. At least one temperature measuring device 40 is
operatively connected to the thermal management system 10, and configured
to measure a temperature 22 of a predetermined portion 24 of the
plurality 20 of battery cells 25. It is to be understood that the
temperature measuring device 40 could be a non-contacting sensor (e.g.,
an IR sensor) or a contacting sensor (e.g., a thermocouple). It is to be
further understood that, as used herein, the predetermined portion 24 may
be a portion of a single cell 25 (e.g., as shown schematically at 24' in
FIG. 1), an entire cell 25 (e.g., as shown schematically at 24'' in FIG.
1), a portion of a group of cells 25 (e.g., as shown schematically at
24''' in FIG. 1), or an entire group of cells 25 (e.g., as shown
schematically at 24'''' in FIG. 1).

[0014] A cell balancing circuit 50 is operatively connected to the
plurality 20 of battery cells 25, and configured to selectively divert a
portion 60 of electric current from at least one of the plurality 20 of
battery cells 25 to the at least one thermoelectric device 30 via an
electronic controller 70. In an example, the portion 60 of electric
current diverted may be between about 0 mA and about 200 mA per battery
cell 25. The electronic controller 70 is operatively connected to the
cell balancing circuit 50, and configured to control a flow 62 of
electric current to the at least one thermoelectric device 30.

[0015] It is to be understood that the battery cell 25 may be any type of
rechargeable electrochemical battery cell. Examples of battery cells 25
contemplated as being within the purview of the present disclosure
include lithium ion battery cells 21 (shown in FIGS. 4 and 5), nickel
metal hydride battery cells, lead-acid battery cells, nickel-cadmium
battery cells, and the like.

[0016] It is to be further understood that battery cells 25 in the
plurality 20 of battery cells 25 may exhibit temperature gradients if no
temperature regulating system is included. Temperature gradients may be
observable through a volume of an individual battery cell 25, or through
a volume of the plurality 20 of battery cells 25. For example, a
particular individual battery 25 may be hotter than the batteries 25 that
surround the particular individual battery 25. In some cases, the
temperature gradient may be according to a predictable pattern. For
example, battery cells 25 in the center of the plurality 20 of battery
cells 25 may tend to be hotter than batteries 25 near an edge of the
plurality 20. In such a case, the temperature of a remote portion of the
plurality 20 of battery cells 25 may be inferred based on an observed
temperature of another portion of the plurality 20 of battery cells 25.
When all of the battery cells 25 in the plurality 20 of battery cells 25
are maintained at substantially the same temperature, all of the battery
cells 25 in the plurality 20 of battery cells 25 will tend to have a
similar useful life.

[0017] As used herein, a battery cell 25 is useful if the amount of
electrical energy storable within the battery cell 25, and releasable by
the battery cell 25 through the battery terminals 38, 39 (as shown in
FIG. 4) is within predetermined limits. As used herein, the term "useful
life" means the duration in which a battery is useful after it is put
into service. The useful life of a rechargeable battery may be expressed
in charge/discharge cycles, units of time, or combinations thereof. It is
to be understood that the useful life of a battery generally depends on
environmental factors including temperature and vibration, as well as
electrical load factors including duration and depth of cycles. It may be
useful to have a standard set of conditions to allow comparison of
batteries. SAE Surface Vehicle Recommended Practice J2288 is an example
of a standardized test method to determine the expected service life, in
cycles, of electric vehicle battery modules.

[0018] As schematically depicted in FIG. 1, the at least one temperature
measuring device 40 may be a non-contacting sensor 42 (e.g., at least one
thermal imaging device, such as an infrared (IR) sensor), a contacting
sensor 44 (e.g., at least one temperature transducer, such as a
thermocouple), or combinations thereof. In an example, an infrared
thermal imaging device 42 may provide a thermal image of the plurality 20
of battery cells 25 with resolution such that a temperature of the
predetermined portion 24 may be determined. In another example, a
temperature transducer 44 such as a thermocouple may be attached to the
predetermined portion 24, thereby measuring (with associated electronics)
the temperature 22 of the predetermined portion 24 of the plurality 20 of
battery cells 25.

[0019] Referring now to FIG. 2, in an example, the electronic controller
70 may be configured to compare (indicated by comparison element 71) the
temperature 22 of the predetermined portion 24 of the plurality 20 of
battery cells 25 to an upper temperature reference 26 and a lower
temperature reference 28. The electronic controller 70 may generate an
upper error value 27 and a lower error value 29 for the predetermined
portion 24 of the plurality 20 of battery cells 25. The upper error value
27 may be generated by finding the difference between the temperature 22
and the upper temperature reference 26. Similarly, the lower error value
29 may be generated by finding the difference between the temperature 22
and the lower temperature reference 28. It is to be understood that
digital and analog techniques may be employed to generate the upper and
lower error values 27, 29.

[0020] The upper temperature reference 26 and the lower temperature
reference 28 may be determined absolutely, or the reference temperatures
26, 28 may be calculated based on operating conditions. In an example of
absolute reference temperatures, the upper temperature reference 26 may
be set at 35° C., and the lower temperature reference may be set
at 10° C. without regard to any real-time measurement. In an
example of calculated references, an average of the temperature 22 of
each battery cell 25 is calculated and is used as a reference temperature
26, 28.

[0021] The electronic controller 70 may include a distribution controller
72 to control the flow 62 of electric current to the at least one
thermoelectric device 30 based on the upper error value 27 and the lower
error value 29 for the predetermined portion 24 of the plurality 20 of
battery cells 25. For example, if the upper error value 27 indicates that
the temperature 22 of the predetermined portion 24 is high, the at least
one thermoelectric device 30 will cool the predetermined portion 24 of
the plurality 20 of battery cells 25. Continuing with the example, if the
upper error value 27 and the lower error value 29 together indicate that
the temperature 22 of the predetermined portion 24 is between the upper
temperature reference 26 and the lower temperature reference 28, no
current will be sent to the at least one thermoelectric device 30.
Continuing further with the example, if the lower error value 29
indicates that the temperature 22 of the predetermined portion 24 is low,
the at least one thermoelectric device 30 will heat the predetermined
portion 24 of the plurality 20 of battery cells 25.

[0022] Referring now to FIG. 3, in an example, the at least one
thermoelectric device 30 may be a Peltier device 32. An example of a
suitable Peltier device 32 may be a Marlow RC12-8 Single-Stage
Thermoelectric Cooler, available from Marlow Industries, Inc., 10451
Vista Park Road, Dallas Tex. 75238-1645. The Peltier device 32 depicted
in FIG. 3 is flat with electrical contacts 33, 33' disposed on an edge 31
of the Peltier device 32.

[0023] FIG. 4 depicts an example of a lithium ion battery cell 21 used in
an example of the battery pack thermal management system 10. The cell 21
shown in FIG. 4 is a flat cell with a positive terminal 38 and a negative
terminal 39. Both terminals 38, 39 are blade terminals. Although a flat
battery cell 21 with blade terminals 38, 39 is depicted in FIG. 4,
batteries of other shapes and terminal styles are also contemplated as
being within the purview of the present disclosure. For example,
cylindrical batteries with end terminals for solderable connections (not
shown) may be used. In examples with cylindrical batteries, a heat sink
(not shown) may improve heat transfer between the cylindrical batteries
and the thermoelectric device 30.

[0024] Also referring now to FIG. 5, the at least one thermoelectric
device 30 may be disposed in thermal contact with at least one thermally
conductive structure 90 opposed to the plurality 20 of battery cells 25.
The example depicted in FIG. 5 shows the at least one thermoelectric
device 30 as having an n-type element 35 and a p-type element 37. The
thermally conductive structure 90 may be, for example, a heat exchanger
or a heat sink (e.g., an aluminum or copper heat sink). The at least one
thermally conductive structure 90 may be disposed in thermal contact with
a heat exchanging fluid 92. It is to be understood that the heat
exchanging fluid 92 may be any suitable fluid, such as for example, air
94 or a liquid coolant 96.

[0025] In an example, a method for battery pack thermal management
includes balancing a voltage of each battery cell 25 in a plurality 20 of
battery cells 25 operatively connected to at least one DC power bus 23.
Balancing may be accomplished, e.g., by shunting a portion 60 of electric
current from at least one of the plurality 20 of battery cells 25 to the
at least one thermoelectric device 30 in thermal contact with a
predetermined portion 24 of the plurality 20 of battery cells 25. The
method further includes determining a temperature 22 of the predetermined
portion 24 of the plurality 20 of battery cells 25.

[0026] Still further, the example of the method includes controlling a
magnitude and direction of the flow 62 of electric current flowing to the
at least one thermoelectric device 30, thereby heating or cooling the
predetermined portion 24 of the plurality 20 of battery cells 25.

[0027] As mentioned above, in an example, the controlling of electric
current flowing to the at least one thermoelectric device 30 may be based
on the upper error value 27 and the lower error value 29 respectively
generated for the predetermined portion 24 of the plurality 20 of battery
cells 25.

[0028] In an example, the portion 60 of electric current flowing to the at
least one thermoelectric device 30 is proportional to the upper error
value 27 or the lower error value 29.

[0029] Further examples may actively transfer heat 80 between the
predetermined portion 24 of the plurality 20 of battery cells 25 and the
at least one thermally conductive structure 90 operatively connected to
the plurality 20 of battery cells 25 through the at least one
thermoelectric device 30. In turn, heat 80 may be transferred between the
at least one thermally conductive structure 90 and a heat exchanging
fluid 92.

[0030] It is to be understood that numerical data have been presented
herein in range format. It is to be understood that this range format is
used merely for convenience and brevity and should be interpreted
flexibly to include not only the numerical values explicitly recited as
the limits of the range, but also to include all the individual numerical
values or sub-ranges encompassed within that range as if each numerical
value and sub-range is explicitly recited. For example, an electric
current range from about 0 mA to about 200 mA should be interpreted to
include not only the explicitly recited limits of about 0 mA and about
200 mA, but also to include discrete current values such as 0.5 mA, 10
mA, 25 mA, 50 mA, 127 mA, etc., and sub-ranges such as 0 mA to 25 mA, 0
mA to 110 mA, etc. Furthermore, when "about" is utilized to describe a
value, this is meant to encompass minor variations (up to +/-5%) from the
stated value.

[0031] Further, it is to be understood that the terms
"connect/connected/connection", "contact/contacting", and/or the like are
broadly defined herein to encompass a variety of divergent
connected/contacting arrangements and assembly techniques. These
arrangements and techniques include, but are not limited to (1) the
direct communication between one component and another component with no
intervening components therebetween; and (2) the communication of one
component and another component with one or more components therebetween,
provided that the one component being "connected to"/"in contact with"
the other component is somehow in operative communication with the other
component (notwithstanding the presence of one or more additional
components therebetween).

[0032] While several examples have been described in detail, it will be
apparent to those skilled in the art that the disclosed examples may be
modified. Therefore, the foregoing description is to be considered
non-limiting.